Co-free corrosion-resistant high-entropy alloy containing ordered phase and preparation method of Co-free corrosion-resistant high-entropy alloy

Abstract

The invention provides a Co-free ordered-phase-containing corrosion-resistant high-entropy alloy and a preparation method thereof, and belongs to the technical field of high-entropy alloy preparation, the chemical component expression of the alloy is (CrFeNi) 100-x-yAlxTiy, the value range of x and y is 5-10, and the atomic numbers of Cr, Fe and Ni are the same. The high-entropy alloy with the components designed in advance is prepared through the vacuum arc melting technology. By adding Al and Ti, the corrosion resistance of the alloy is greatly improved compared with that of a CrFeNi entropy alloy with a single-phase FCC structure. Wherein the (CrFeNi) 90Al5Ti5 alloy has excellent corrosion resistance, and the corrosion resistance is superior to that of most of high-entropy alloys and most of conventional alloys. In addition, the high-entropy alloy does not contain precious metal Co, so that the high-entropy alloy has potential engineering application value.

Description

Technical Field

[0001] The invention relates to the field of high entropy alloys, in particular to a Co-free, ordered phase-containing corrosion-resistant high entropy alloy and a preparation method thereof. Background Art

[0002] Compared with traditional alloys, the new high entropy alloy design paradigm provides huge composition opportunities for high-performance materials. Due to the excellent properties of reported high entropy alloys such as oxidation resistance, high strength, wear resistance and corrosion resistance, high entropy alloys have attracted more and more attention from scholars and are favored in the industrial field. Although a variety of elements are doped in high entropy alloys, high entropy alloys (HEAs) mainly exhibit simple solid solution structures due to the high entropy effect. The comprehensive properties of single-phase high entropy alloys are generally poor and cannot meet the requirements of practical engineering applications. Therefore, the formation of dual phases in high entropy alloys is an effective solution to make up for the shortcomings of single phases and use dual phases to develop high entropy alloys with good performance. High entropy alloys also provide clues for the derivation of anti-corrosion materials, which is of great significance for the marine application of structural alloys. Adding alloying elements is generally considered to be an effective way to obtain new dual-phase high corrosion resistant high entropy alloys, such as Al, Cr, Ni, Ti and Nb. For dual phases, especially ordered phases, precipitation strengthening has been widely recognized.

[0003] At present, some researchers have conducted some research on the corrosion behavior of HEAs due to the L21 phase precipitation. Due to the increased stability of the passivation film, the L21 phase can improve the local corrosion resistance of the passivation film. The researchers found that after the L21 phase is strengthened, the CrFeNiAl 0.35 Si 0.1 Ti 0.1 High entropy alloys show excellent corrosion resistance in 3.5% NaCl solution, close to super stainless steel. It can be seen that research on L21 phase-strengthened high entropy alloys is precious and rare. In addition, most corrosion-resistant high entropy alloys generally contain Co, and Co is expensive, more than six times higher than Cr, Fe, Ni, etc., which makes the manufacturing cost of high entropy alloys high, hindering the industrial application of high entropy alloys. Therefore, while ensuring the corrosion resistance of high entropy alloys, reducing the content of Co in high entropy alloys to reduce the alloy manufacturing cost and promote the engineering application of high entropy alloys is a technical problem that needs to be solved urgently. Summary of the invention

[0004] The purpose of the present invention is to provide a Co-free, ordered phase-containing corrosion-resistant high-entropy alloy and a preparation method thereof, so as to solve the technical problem of high cost of Co-containing highly corrosion-resistant high-entropy alloys.

[0005] The present invention is achieved in that:

[0006] The present invention provides a Co-free, corrosion-resistant high-entropy alloy containing an ordered phase, wherein the alloy comprises: Cr, Fe, Ni, Al and Ti; the atomic percentages of the metal elements of the high-entropy alloy are as follows: Cr: 26.6-30.0%, Fe: 26.6-30.0%, Ni: 26.6-30.0%, Al: 5.0-10.0%, Ti: 5.0-10.0%. The high-entropy alloy is expressed by a chemical formula of (CrFeNi) 100-x-y Al x Ti y , x and y range from 5 to 10, and Cr, Fe and Ni have the same atomic number.

[0007] As the Al and Ti contents of the alloy increase, the microstructure of the alloy gradually transforms from a three-phase structure consisting of FCC phase, BCC phase and L21 ordered phase to a two-phase structure of BCC and L21. 80 Al 10 Ti 10 The microstructure of the alloy consists of two phases: BCC phase and L21 ordered phase. 85 Al 8 Ti 7 and (CrFeNi) 90 Al 5 Ti 5 The microstructure of the alloy consists of three phases: FCC phase, BCC phase and L21 ordered phase.

[0008] On the other hand, the present invention also provides a method for preparing the above-mentioned Co-free corrosion-resistant high-entropy alloy containing an ordered phase, using a vacuum arc melting technique to prepare a high-entropy alloy (CrFeNi) with a pre-designed composition. 100-x-y Al x Ti y The method comprises:

[0009] Step (1), calculating the mass of each metal element according to the molar ratio and weighing high-purity Cr, Fe, and Ni metal elements;

[0010] Step (2), placing the Cr, Fe, and Ni metal elements weighed in step (1) in a copper crucible in a smelting furnace in order from low to high melting points;

[0011] Step (3), after the smelting furnace is evacuated, it is filled with high-purity inert protective gas to remove residual oxygen, and then it is powered on for repeated smelting, and cooled in a water-cooled copper mold to obtain an equiatomic CrFeNi alloy button ingot;

[0012] Step (4), calculating the masses of the CrFeNi alloy and Al and Ti according to the set molar ratios of Cr, Fe, Ni to Al and Ti in the equiatomic CrFeNi alloy, and weighing the equiatomic CrFeNi alloy and high-purity Al and Ti metal elements;

[0013] Step (5), placing the equiatomic CrFeNi alloy and high-purity Al and Ti metal elements weighed in step (4) in a copper crucible in a smelting furnace in sequence;

[0014] Step (6), after the smelting furnace is evacuated, it is filled with high-purity inert protective gas to remove residual oxygen, and then the smelting is repeated by powering on, and the alloy button ingot is cooled in a water-cooled copper mold, which is a corrosion-resistant high-entropy alloy without Co and containing an ordered phase.

[0015] Preferably, in steps (1) and (4), the purity of each of the metal single substances Cr, Fe, Ni, Al and Ti raw materials is ≥99.95%.

[0016] Preferably, in steps (3) and (6), the protective gas is argon, and the vacuum degree in the smelting furnace is 5×10 -3 The protective gas is filled in at 1.5 Pa.

[0017] Preferably, in steps (3) and (6), electric melting of pure titanium ingots is performed before electric melting of the elemental metal to remove residual oxygen.

[0018] Preferably, in steps (3) and (6), the number of repeated smelting is 5 times, and the time of each smelting is 3 minutes.

[0019] The beneficial effects of the present invention are as follows:

[0020] 1. The present invention provides a Co-free corrosion-resistant high entropy alloy (CrFeNi) 100-x-y Al x Ti y The alloy does not contain expensive metal Co, which greatly reduces the cost of alloy preparation.

[0021] 2. Co-free corrosion-resistant high entropy alloy (CrFeNi) provided by the present invention 100-x-y Al x Ti y When x=5, y=5, (CrFeNi) with excellent corrosion resistance can be obtained. 90 Al 5 Ti 5 The alloy of the present invention has a lower corrosion current density (79nA·cm -2 ) and a wider passivation region (1200mV Ag / AgCl), which is superior to most high entropy alloys and most conventional alloys.

[0022] 3. The Co-free high entropy alloy provided by the present invention has excellent corrosion resistance, and the emergence of the L21 ordered phase has important research value.

[0023] Based on the above reasons, the present invention has engineering application value and can be widely promoted in the field of metal materials and their preparation. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is the XRD phase analysis diagram of the high entropy alloy prepared in Examples 1 to 3 of the present invention.

[0025] Figure 2 It is a schematic diagram of the surface morphology of the high entropy alloys prepared in Examples 1 to 3 of the present invention.

[0026] Figure 3 It is a high-resolution schematic diagram of the high entropy alloys prepared in Examples 1 to 3 of the present invention.

[0027] Figure 4 It is the corrosion resistance electrochemical curve diagram of the high entropy alloy prepared in Examples 1 to 3 of the present invention. DETAILED DESCRIPTION

[0028] In order to more clearly illustrate the technical solution of the present invention, the technical solution in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the specification. Obviously, the described embodiment is only a part of the embodiment of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and does not constitute any limitation on the present invention and its application or use.

[0029] The object of the present invention is to provide a Co-free corrosion-resistant high-entropy alloy containing an ordered phase. By adding metal elements Al and Ti to a CrFeNi medium-entropy alloy with a single-phase FCC structure, a three-phase structure of an FCC phase, a BCC phase and an L21 ordered phase is formed in the alloy. The alloy has corrosion resistance similar to that of a Co-containing high-entropy alloy, and because it does not contain the Co element, its preparation cost is lower, providing a solution for developing low-cost high-entropy alloys with engineering application potential.

[0030] The invention provides a Co-free corrosion-resistant high-entropy alloy containing an ordered phase, wherein the alloy comprises: Cr, Fe, Ni, Al and Ti; the atomic percentages of the metal elements of the high-entropy alloy are as follows: Cr: 26.6-30.0%, Fe: 26.6-30.0%, Ni: 26.6-30.0%, Al: 5.0-10.0%, and Ti: 5.0-10.0%. As the Al and Ti contents of the alloy increase, the microstructure of the alloy is gradually transformed from a three-phase structure consisting of an FCC phase, a BCC phase and an L21 ordered phase to a two-phase structure of BCC and L21.

[0031] The Co-free, ordered-phase-containing corrosion-resistant high-entropy alloy and its preparation method of the present invention are described in detail below in conjunction with specific embodiments.

[0032] Example 1

[0033] The Co-free, ordered-phase-containing corrosion-resistant high-entropy alloy provided in this embodiment comprises the following components: Cr, Fe, Ni, Al and Ti; the atomic percentages of the metal elements in the alloy are as follows: Cr: 26.6%, Fe: 26.6%, Ni: 26.6%, Al: 10.0%, Ti: 10.0%.

[0034] The preparation method of the corrosion-resistant high-entropy alloy without Co and containing an ordered phase in this embodiment comprises the following steps:

[0035] Step (1), according to the molar ratio of Cr, Fe and Ni being 1:1:1, the mass of each metal element is calculated and the Cr, Fe and Ni metal elements with a purity greater than or equal to 99.95% are weighed.

[0036] Step (2), placing the Cr, Fe, and Ni metal elements weighed in step (1) in a copper crucible in a smelting furnace in order from low to high melting points.

[0037] Step (3), after the smelting furnace is evacuated, the vacuum degree in the smelting furnace is 5×10 -3 High-purity inert protective gas (such as argon) is filled at 4000 ℃ and 7500 ℃. Before melting the elemental metal by electricity, pure titanium ingot is melted by electricity to remove residual oxygen. After removing the residual oxygen, the melting is repeated by electricity for 5 times, each melting time is 3 minutes, and the equiatomic CrFeNi alloy button ingot is obtained by cooling in a water-cooled copper mold.

[0038] Step (4), according to the molar ratio of Cr, Fe, Ni to Al, Ti in the equiatomic CrFeNi alloy of 26.6:26.6:26.6:10.0:10.0, the masses of the equiatomic CrFeNi alloy and the metals Al and Ti are calculated, and the equiatomic CrFeNi alloy and high-purity Al and Ti metal elements are weighed. The purity of the high-purity Al and Ti metal elements is also greater than or equal to 99.95%.

[0039] Step (5), placing the equiatomic CrFeNi alloy and high-purity Al and Ti metal elements weighed in step (4) in a copper crucible in a smelting furnace in sequence.

[0040] Step (6), after the smelting furnace is evacuated, the vacuum degree in the smelting furnace is 5×10 -3 Pa, high-purity inert protective gas is filled in; before electric melting, pure titanium ingots are melted by electric melting to remove residual oxygen; after removing the residual oxygen, electric melting is repeated, and the melting is repeated 5 times, each melting time is 3 minutes, and the alloy is cooled in a water-cooled copper mold to obtain a Co-free, ordered phase-containing corrosion-resistant high-entropy alloy.

[0041] Example 2

[0042] The Co-free, ordered phase-containing corrosion-resistant high-entropy alloy provided in this embodiment comprises: Cr, Fe, Ni, Al and Ti; the atomic percentages of the metal elements in the alloy are as follows: Cr: 28.3%, Fe: 28.3%, Ni: 28.3%, Al: 8.0%, Ti: 7.0%. The preparation method thereof can refer to the preparation method of the above-mentioned embodiment 1.

[0043] Example 3

[0044] The Co-free, ordered phase-containing corrosion-resistant high-entropy alloy provided in this embodiment comprises: Cr, Fe, Ni, Al and Ti; the atomic percentages of the metal elements in the alloy are as follows: Cr: 30.0%, Fe: 30.0%, Ni: 30.0%, Al: 5.0%, Ti: 5.0%. The preparation method thereof can refer to the preparation method of the above-mentioned embodiment 1.

[0045] The high entropy alloys prepared in Examples 1 to 3 were analyzed using an X-ray diffractometer. The high entropy alloys were mounted into samples with a size of Φ5mm×5mm using a metallographic mounting machine. The sample surfaces were smoothed using 400#, 1000#, 1500#, and 2000# metallographic sandpapers, and then the samples were polished. The X-ray diffraction spectrum of the high entropy alloy was measured using an X-ray diffractometer, with a scanning angle range of 20° to 100° and a scanning speed of 4° / min. The results are shown in FIG. Figure 1As shown in the figure, it can be seen that both Example 2 and Example 3 show a combination of FCC and BCC phases. As the Al and Ti contents increase, the FCC phase peak intensity decreases and the BCC phase peak intensity increases. This transition leads to a transition from a two-phase structure (FCC+BCC) to a single-phase BCC structure. In addition, some small peaks are detected in Example 2, showing an ordered L21 phase.

[0046] The structure of the prepared samples was observed using a scanning electron microscope. Figure 2 As shown. Figure 2 It can be seen that Example 1 can show obvious eutectic morphology. Example 2 is mainly composed of bright irregular BCC phase with FCC phase area, indicating that the microstructure is different from that of Example 1. Precipitates of different sizes are evenly distributed in the BCC phase. Similar to Example 2, two regions can be seen in Example 3, namely the dark gray FCC phase and the light gray BCC phase. As the Al and Ti contents increase, the proportion of the BCC phase increases.

[0047] The samples prepared in Examples 1 to 3 were ground to 25 μm and observed using a transmission electron microscope. They were then subjected to a double-jet electrolytic polishing process at liquid nitrogen temperature. The polishing solution was a mixture of 6 vol% perchloric acid and 94 vol% methanol. The results are shown in Figure 2. Figure 3 As shown, through Figure 3 It was confirmed that Examples 1 and 3 also had the ordered phase L21.

[0048] The corrosion and passivation behaviors were tested at room temperature by an electrochemical workstation (CHI760E). A three-electrode system was used, and the working electrode was a sample sealed in a Teflon mold with an exposed area of ​​1 cm 2 The surface area of ​​the counter electrode is 15×15mm 2 The reference electrode is a Pt electrode (Ag / AgCl / Cl - , αCl - =1 mol / L, E = 0.2224 V vs. SHE), the electrolyte is 3.5 wt.% NaCl solution. Each test was repeated at least 3 times to ensure accuracy. Figure 4 The potentiodynamic polarization curves of the high entropy alloys prepared in Examples 1 to 3 are shown in the figure. As can be seen from the figure, the three alloys all show similar active-passive processes, and seem to directly transform from the Tafel zone to the stable passivation zone without active-passive transformation. This indicates that the growth of the passivation film at the corrosion potential is spontaneous.

[0049] Table 1 below lists various electrochemical parameters extracted from the polarization curves, including the passivation breakdown potential (E b ), corrosion potential (E corr), passivation zone (ΔE p =E b -E corr ) and corrosion current density (I corr ). Since the corrosion current density is proportional to the corrosion rate, when corrosion occurs at E corr When the corrosion current density of Example 3 is lower than that of Example 3, it is more corrosion resistant. More importantly, Example 3 shows a greater E b and a wider ΔE p Since ΔE p It is usually related to the stability of the passive film on the metal surface, so the wide passive region indicates that the passive film of the alloy of the present invention is quite stable. b As an indicator of the alloy's resistance to pitting corrosion in electrolyte solutions, E b The larger the value, the stronger the alloy's pitting resistance.

[0050] Therefore, the corrosion resistance order shown by the electrochemical parameters is: Example 3> Example 2> Example 1.

[0051] Table 1 Electrochemical parameters of high entropy alloys prepared in Examples 1 to 3

[0052] alloy <![CDATA[I corr (nA cm -2 )]]> <![CDATA[E corr (mV Ag / AgCl )]]> <![CDATA[E b (mV Ag / AgCl )]]> <![CDATA[ΔE p (mV Ag / AgCl )]]> Example 1 208 -218 243 461 Example 2 98 -174 998 1172 Example 3 79 -173 1027 1200

[0053] It can be seen that adding a small amount of Al and Ti to the CrFeNi medium entropy alloy can produce a corrosion-resistant high entropy alloy containing a sequence phase, which has extremely high research value and does not contain expensive Co, so it has engineering application value. However, excessive addition will cause the alloy to gradually lose the FCC phase, further leading to a decrease in the corrosion resistance of the alloy.

[0054] Comparative Example 1

[0055] The Co-free high entropy alloy provided in this comparative example comprises: Cr, Fe, Ni, Al and Ti; the atomic percentage of each metal element in the alloy is as follows: Cr: 15.0%, Fe: 47.0%, Ni: 28.0%, Al: 5.0%, Ti: 5.0%. The preparation method thereof can refer to the preparation method of the above-mentioned embodiment 1.

[0056] The alloy obtained in Comparative Example 1 was tested and found that its corrosion resistance was not as good as that of the alloy in Experimental Example 3.

[0057] Comparative Example 2

[0058] The Co-free high-entropy alloy provided in this comparative example comprises the following components: Cr, Fe, Ni, Al and Ti; the atomic percentages of the metal elements in the alloy are as follows: Cr: 26.6%, Fe: 26.6%, Ni: 26.6%, Al: 10.0%, Ti: 10.0%.

[0059] The preparation method thereof comprises the following steps:

[0060] Step (1), according to the molar ratio of Cr, Fe, Ni, Al, Ti being 26.6:26.6:26.6:10.0:10.0, the mass of each metal element is calculated and Cr, Fe, Ni, Al and Ti metal elements with a purity greater than or equal to 99.95% are weighed.

[0061] Step (2), placing the Cr, Fe, Ni, Al and Ti metal elements weighed in step (1) in a copper crucible in a smelting furnace in order from low to high melting points.

[0062] Step (3), after the smelting furnace is evacuated, it is filled with high-purity inert protective gas to remove residual oxygen, and then it is powered on for repeated smelting, and cooled in a water-cooled copper mold to obtain a Co-free high-entropy alloy.

[0063] After testing the alloy in Comparative Example 2, it was found that its corrosion resistance was not as good as that of the alloy in Experimental Example 1.

Claims

1. A Co-free, corrosion-resistant high-entropy alloy containing an ordered phase, characterized in that: The alloy components include: Cr, Fe, Ni, Al and Ti; the atomic percentages of the metal elements of the high entropy alloy are as follows: Cr: 26.6-30.0%, Fe: 26.6-30.0%, Ni: 26.6-30.0%, Al: 5.0-10.0%, Ti: 5.0-10.0%.

2. The Co-free, ordered phase-containing corrosion-resistant high-entropy alloy according to claim 1, characterized in that: The atomic percentages of Cr, Fe and Ni are the same.

3. The Co-free, ordered phase-containing corrosion-resistant high-entropy alloy according to claim 2, characterized in that: The atomic percentages of the metal elements of the high entropy alloy are as follows: Cr: 30.0%, Fe: 30.0%, Ni: 30.0%, Al: 5.0, Ti: 5.

0.

4. The method for preparing the Co-free, ordered phase-containing corrosion-resistant high-entropy alloy according to claim 1, characterized in that: The steps include: (1) Calculate the mass of Cr, Fe and Ni according to the molar ratio of Cr, Fe and Ni being 1:1:1, and weigh high-purity Cr, Fe and Ni metal elements; (2) placing the Cr, Fe, and Ni metal elements weighed in step (1) in a copper crucible in a smelting furnace in order of their melting points from low to high; (3) After the melting furnace is evacuated, it is filled with inert protective gas, and then the residual oxygen is removed, and the melting is repeated by power supply, and finally cooled in a water-cooled copper mold to obtain an equiatomic CrFeNi alloy; (4) According to the chemical formula (CrFeNi) 100-x-y Al x Ti y The proportion of each element in the formula is used to calculate the mass required for the equiatomic CrFeNi alloy and Al and Ti, and then the equiatomic CrFeNi alloy and Al and Ti metal elements are weighed; wherein the value range of x and y is 5 to 10; (5) placing the equiatomic CrFeNi alloy and Al and Ti metal elements weighed in step (4) in a copper crucible in a smelting furnace in sequence; (6) After the melting furnace is evacuated, it is filled with inert protective gas, and then the residual oxygen is removed. Then, the melting is repeated by power-on, and the alloy is cooled in a water-cooled copper mold to obtain a Co-free, ordered phase-containing corrosion-resistant high-entropy alloy.

5. The method for preparing the Co-free, ordered phase-containing corrosion-resistant high-entropy alloy according to claim 4, characterized in that: In steps (3) and (6), the smelting is repeated 5 times, and the time of each smelting is 3 minutes.

6. The method for preparing the Co-free, ordered phase-containing corrosion-resistant high-entropy alloy according to claim 4, characterized in that: In steps (3) and (6), the inert protective gas is argon, and the vacuum degree in the smelting furnace is 5×10 -3 Pa is filled with inert protective gas.

7. The method for preparing the Co-free, ordered phase-containing corrosion-resistant high-entropy alloy according to claim 4, characterized in that: In step (4), the values ​​of x and y are both 5.

8. The method for preparing the Co-free, ordered phase-containing corrosion-resistant high-entropy alloy according to claim 4, characterized in that: In steps (3) and (6), the pure titanium ingot is first electrically melted before the electrical melting to remove residual oxygen.

9. The method for preparing the Co-free, ordered phase-containing corrosion-resistant high-entropy alloy according to claim 4, characterized in that: In steps (1) and (4), the purity of the metal single substance Cr, Fe, Ni, Al and Ti raw materials is ≥99.95%.

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